1. Field of the Invention
The present invention relates to a through-the-lens ("TTL") automatic light adjustment control device for a camera which pre-emits a light prior to a main light emission during exposure and, in particular, a TTL automatic light adjustment control device which controls an amount of light emission of a main light emission, during exposure, based on information regarding a reflected light distribution of a subject field detected during a pre-emission of light.
2. Description of the Related Art
So-called TTL automatic light adjustment photography executes control during flash photography. A flash emission is begun immediately after a shutter of a camera opens. Light reflected from the subject arrives at a film surface, through a photographic lens. Light reflected by the film surface is captured by a photoelectric conversion unit within a mirror box of the camera and is converted to electric signals, at a specified amplification rate determined by the film sensitivity. The electric signals are then integrated with a condenser. The output of the condenser is compared with a specified value, and the flash emission is terminated at the point in time when the output of the condenser equals the specified value.
"TTL multi-light adjustment" technology, which is a type of TTL automatic light adjustment control system has evolved in recent years. Such technology is disclosed in Japanese Laid-Open Patent Publication Number Hei 3-68928. Multiple photoelectric conversion units, capable of measuring light by dividing a subject field into multiple areas, are arranged in a position to watch a film plane. A flash is pre-emitted, prior to opening a focal plane shutter. The light reflected by the subject image on the shutter curtain surface is captured by the multiple photoelectric conversion unit. Each output of the multiple photoelectric conversion units is individually integrated generating subject field reflected light distribution information for each region based on the light pre-emission. To obtain an optimum exposure for the main subject, the weighing of each separate region is based on a specified algorithm for processing the subject field reflected light distribution information, as detected for each region.
A main flash is thereafter emitted immediately after the shutter has opened. Light reflected by the film plane is captured by the same multiple photoelectric conversion unit. The output of the photoelectric conversion unit is given predetermined weights and integrated. The main flash emission is terminated when the integrated output matches a specified value.
The light pre-emission in Japanese Laid-Open Patent Publication Number Hei 3-68928 is for detecting, in advance, information on the subject field reflected light distribution. Further, a judgement is made as to whether each separate field measured should be emphasized during the main light emission. It is therefore necessary for the control device to determine the amount of flash emission (amount of light pre-emission) that is illuminated as the light pre-emission. A repeated light emission system has been proposed for this purpose.
In the proposed repeated light emission system, when a light pre-emission command signal is input, a single small light pre-emission, with a known amount of light, is executed. A camera control device repeatedly outputs the light pre-emission command signal, and stops the light pre-emission command when the integrated output of each separate region has reached a predetermined level. The camera control device counts the number of times the light pre-emission command is given, and derives the amount of total light emission of the light pre-emission from the count and the known amount of light pre-emission per light emission.
Nonetheless, when using this proposed repeated light emission system, the control circuit for repeatedly conducting the small light quantity light pre-emission is rather complicated. The space and cost added by this control circuit, inhibits the designing and making of a compact, low cost camera. In particular, when designing a camera body that incorporates a flash, this problem is presumably insurmountable. In a camera which incorporates a flash, it has heretofore not been possible to mount a TTL multi-light adjustment unit. Moreover, with a light pre-emission that is based on a repeated light emission system, because the number of light emissions may become large, depending on the subject field conditions, and because each emission cannot be shorter than a given specified time, due to circuit limitations, the light pre-emission can take a long time, for example, about 3 ms. Thus, the time from when the mirror has been brought up until releasing the front blind of the shutter is increased and the camera release operation cannot be conducted at high speed.